The present invention relates to converting an analog input into a digital output, and more particularly, to a delta-sigma analog-to-digital converter with innovative designs of the loop filter, the quantizer, the digital-to-analog converter, and/or the operational amplifier(s) included therein.
In today's world, the market for information and communication technology is expanding as never before. Not surprisingly, wireless communication has become more and more important. Nowadays, a variety of wireless communication systems have been developed. In general, the wireless signals are received by an antenna, and the desired frequency band is selected from the received spectrum. Next, the selected frequency band undergoes a plurality of signal processing stages, including analog filtering, amplification, demodulation, analog-to-digital conversion, etc. Further signal processing is done in the digital domain by a digital circuit, such as a digital signal processor (DSP).
Important trends in the receiver design for wireless communication applications are: smaller product size, lower product cost and longer stand-by time. Products can be made smaller and cheaper by increasing the level of integration. This means on-chip integration of external components, such as inductors and filters. Thus, an important role can be played by an analog-to-digital converter (ADC) implemented in the receiver. More specifically, shifting the ADC towards the antenna side of the receiver would allow more digital integration of (external) analog functions on a single chip. However, this requires the implemented ADC with high linearity, dynamic range and bandwidth capabilities.
Continuous-time delta-sigma modulation is a good technique for analog-to-digital conversion as it incorporates inherent anti-aliasing filtering, excellent linearity performance, and low-power capability. Therefore, a continuous-time delta-sigma analog-to-digital converter manifests itself in a wireless communication system, such as a GSM/WCDMA system, as an indispensable building block. In this way, most part of the front-end gain adaptation and blocker filtering can be dealt with in the DSP which is robust and scalable.
In view of above, how to design a continuous-time delta-sigma analog-to-digital converter satisfying requirements of a designated application, such as a wireless communication receiver, becomes a challenge to the circuit designer.